Deposition of tungsten-containing materials is an integral part of many semiconductor fabrication processes. These materials may be used for horizontal interconnects, vias between adjacent metal layers, contacts between first metal layers and devices on the silicon substrate, and high aspect ratio features. In a conventional tungsten deposition process on a semiconductor substrate, the substrate is heated to the process temperature in a vacuum chamber, and a very thin portion of tungsten film which serves as a seed or nucleation layer is deposited. Thereafter, the remainder of the tungsten film (the bulk layer) is deposited on the nucleation layer. The bulk layer is generally deposited more rapidly than the nucleation layer.
Increasingly thin tungsten electrical connects having very low resistance will enable smaller critical dimension devices. Although conventional methods are able to deposit nucleation layers, their ability to provide nucleation layers for the deposition of low resistivity tungsten in small critical dimension features is limited. For example, the formation of logic contacts has become more challenging as aspect ratios grow to more than 10:1. Void-free fill in aggressive features like these is problematic using conventional tungsten deposition techniques.